JP3771785B2

JP3771785B2 - Optical amplifier

Info

Publication number: JP3771785B2
Application number: JP2000254259A
Authority: JP
Inventors: 俊樹菅原
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2000-08-21
Filing date: 2000-08-21
Publication date: 2006-04-26
Anticipated expiration: 2020-08-21
Also published as: US20020021488A1; US6388804B1; JP2002064235A

Description

【０００１】
【発明の属する技術分野】
本発明は、光通信システムにおいて用いる光増幅装置、特に波長多重による光伝送方式を採用したシステムに適用して好適な光増幅装置に関する。
【０００２】
【従来の技術】
近年、光増幅装置を中継器として用いる光伝送システムの研究・実用化が盛んである。特に、インターネットを中心としたマルチメディアサービスに対応するために、波長の異なる複数の信号光を多重化するＷＤＭ（Wavelength Division Multiplex）による大容量化が有効である。このＷＤＭ技術を用いた光通信システムにおいては、伝送距離を拡大するために全ての信号光を一括して増幅する光中継増幅器の果たす役割が非常に大きい。
【０００３】
この光増幅装置を構成するための光増幅媒体として、希土類を添加した光ファイバが有効であり、現在研究並びに実用化が進められている。特にエルビウム添加ファイバ（以下「ＥＤＦ（Erbium-Doped Fiber）」という）は、光ファイバが低損失となる波長の広い範囲で増幅作用を持つため、光ファイバ通信システムに広く利用されている。
【０００４】
光増幅媒体に信号光波長帯域での増幅作用を持たせるため、光増幅媒体に信号光より短い波長の励起光が信号光と共に入射される。そして、信号光と励起光を効率よく光増幅媒体に入射するため、光増幅媒体の端にＷＤＭ光カプラが接続される。
【０００５】
しかし、希土類添加光ファイバがＷＤＭ信号光を一括して増幅する際、利得が波長依存性を持たない領域が狭い上、波長範囲を限定しただけでは入力信号光パワーの変化により波長依存性が生じてしまう。この解決方法として、光増幅媒体の入力パワーと出力パワーを測定し、その測定値から求めた平均利得が一定となるよう励起光のパワーを調整する利得一定制御（Automatic Gain Control：ＡＧＣ）によって、異なる入力パワーにおける利得の波長依存性を抑えられることが知られている。この方法を用いた光増幅装置では、更に可変光減衰器を用いた出力一定の制御が採用される。
【０００６】
しかし、実際の光増幅装置においては、入力パワーの他に温度によっても利得特性が変化する。このため、ある温度において利得の波長依存性が小さくなるように光増幅装置が設計されたものであっても、ＡＧＣによる制御だけでは使用時の温度変化により波長依存性が生じることが避けられない。
【０００７】
この問題を解決するために、光増幅装置の利得を波長で均一に維持する技術が幾つか知られている。例えば、特開平４−１１７９４号公報に開示されている技術によれば、ペルチエ素子等の温度制御デバイスを用いて光増幅媒体の温度を一定に制御する。これにより、光増幅装置の利得が波長で均一になる。また、特開平１０−３３５７２２号公報に開示された技術によれば、サーミスタを用いて温度を測定し、温度に応じて光透過素子の特性を制御することで利得の波長依存性が補正される。
【０００８】
【発明が解決しようとする課題】
しかし、上記従来例では、以下のような課題がある。例えば、ペルチエ素子等の温度制御デバイスを用いる方式では、消費電力が大きくなることが避けられるず、更にペルチエ素子を動作させることよって生じる発熱を放出するために装置が複雑かつ大型になる。また、サーミスタと光透過素子を用いて利得の波長依存性を補正する方式では、入力パワー或いは温度の変化によって生じるＥＤＦの利得の波長依存性を十分に補正するための光透過素子の実現が難しい。また、温度をパラメータに加える補正になるため、部品数が増え、制御方法が複雑になることが避けられない。
【０００９】
本発明の目的は、上記の従来技術の有する課題を解決し、入力光パワー及び温度が変化しても利得の波長依存性を生じないようにすることが可能な、消費電力が小さく、かつ部品数の少ない簡易な構成の光増幅装置を提供することにある。
【００１０】
【課題を解決するための手段】
本発明者は、希土類添加ファイバに関する実験の結果から、入力光パワー及び温度を種々変えた場合の、利得の波長依存性を一定にした状態、即ち波長間の利得偏差が一定の状態での出力光パワーと励起光パワーの関係を表す特性曲線が単純な単調増加関数乃至線形関数となること、更に出力光パワーと励起光パワーとがこれらの関数による特性曲線上に乗った関係に保たれていれば、入力光パワー及び温度が変化しても波長依存性が変化しない利得特性が得られることを見い出した。従って、利得偏差のない状態の特性曲線を採用し、出力光パワーと励起光パワーとをその特性曲線に乗った関係にすれば、利得偏差のない光増幅器を得ることができる。以上について後で詳述する。なお、入力光に利得偏差がある場合、その逆の偏差の特性曲線を採用し、出力光パワーと励起光パワーをその特性曲線に乗った関係にすれば、光増幅器からは利得偏差のない出力光を得ることができる。
なお、「利得偏差が一定の状態」には、例えば、図２に示す状態をいう。ここで利得偏差の値は、図２ (a) に示すように、負の値を取る場合（例えば、（最大波長の利得）−（最小波長の利得）で偏差を定義した場合。以下、同じ。）と図２ (c) に示すように、正の値を取る場合とがある。図２ ( ｂ ) に示す場合は、 (a) 、 (c) の特別の場合で、利得偏差が一定または０の場合をいう。
また、上述の特性曲線の「曲線」には直線を含む。
【００１１】
本発明は、そのような知見に基づいてなされたものである。即ち、本発明の前記課題は、波長多重の各信号光の利得偏差が一定の状態での、光増幅媒体の励起光パワーと出力光パワーの関係を表す特性曲線を収納した特性情報テーブルを用意しておき、光増幅媒体の出力光パワーと励起光パワーが特性曲線で与えられた関係に従うように励起光パワーを制御する励起光制御部を備えることによって効果的に解決することが可能である。そのような手段を採用すれば、出力光パワーと励起光パワーが特性曲線に従う関係が維持され、入力光パワー及び環境温度が変化しても、波長依存性のない利得特性を得ることができるからである。
【００１２】
具体的に、本発明の第１の光増幅装置は、励起光の入射によって入力光を増幅する光増幅媒体と、上記励起光を発生する光源と、励起光のパワーを制御する励起光制御部とを有しており、当該励起光制御部は、入力光を構成する波長の間の利得偏差が一定の状態での、光増幅媒体の出力光パワーと励起光パワーとの関係を収納した特性情報テーブルと、光増幅媒体が増幅して得た出力光のパワーの値を特性情報テーブルに照合して引き出した励起光のパワーの値を用いて光源を制御し、光源の励起光のパワーを上記引き出した励起光のパワーにする光源制御部を備えていることを特徴とする。
【００１３】
入力光に波長依存性がなくてもそのパワーが変化して到来する場合がある。そのような場合には、光増幅装置に減衰量可変の光減衰器を配置し、当該光減衰器の減衰量を出力光パワーが一定となるように制御する構成を採用することが効果的となる。
【００１４】
本発明の第２の光増幅装置は、出力光パワーを一定にする実施形態で、第１の光増幅装置に、更に、光増幅媒体の出力光に減衰を与えて出力する減衰量可変の光減衰器と、当該光減衰器の出力光パワーの検出結果を使って光減衰器の出力光が所定のパワーとなるように光減衰器の減衰量を制御する減衰量制御部とを備えることを特徴とする。
【００１５】
本発明の第３の光増幅装置は、出力光パワーを一定にする別の実施形態で、第１の光増幅装置に、更に、光増幅媒体の出力光に減衰を与えて出力する減衰量可変の光減衰器と、光増幅媒体の出力光パワーの検出結果を使って光減衰器の出力光が所定のパワーとなるように光減衰器の減衰量を制御する減衰量制御部とを備えることを特徴とする。
【００１６】
第２及び第３の構成では、光増幅装置の出力光パワーを光減衰器の減衰量だけ高めておくことになる。光増幅装置が光ファイバを駆動する場合、出力光パワーが大きいことが要求され、その消費電力も大きくなるので、上記減衰量が負担となる場合がある。そのような場合には、光増幅装置を前段と後段の２個の光増幅装置で構成し、その中間に光減衰器を配置することが効果的となる。前段光増幅装置には出力光パワーへの制約は軽度であり、減衰量は負担とならない。
【００１７】
本発明の第４の光増幅装置は、そのような前段と後段の２段構成にした実施形態で、上記の光増幅装置が光増幅部となり、その２個の光増幅部が減衰量可変の光減衰器を間に介して縦続に接続されて前段と後段となり、後段の光増幅部の出力光が所定のパワーとなるように後段の光増幅部の出力光パワーの検出結果を使って光減衰器の減衰量を制御する減衰量制御部が後段の光増幅部の出力側に接続されていることを特徴とする。
【００１８】
第４の光増幅装置において出力光が所定のパワーとなるため、後段の光増幅部の励起光パワーは一意的に決定しても良く、固定化することが可能となる。
【００１９】
本発明の第５の光増幅装置は、後段の光増幅部の特性情報テーブルから引き出す励起光のパワーの値を所定の出力光パワーの値に対応させた励起光のパワーの値にすることにより、後段の光増幅部の励起光パワーを固定化することを特徴とする。
【００２０】
入力光のパワーが比較的大きい場合には、第５の光増幅装置において、前段の増幅部を省略することが可能になる。
【００２１】
本発明の第６の光増幅装置は、第５の光増幅装置における光減衰器と後段の光増幅部とによって構成されることを特徴とする。
【００２２】
また、光伝送システムにおいて、高い増幅率を要求される場合（例えば、光ファイバの中継間隔が長く設定される場合など）がある。そのような場合には、複数の光増幅装置を縦続接続する構成を採用することが効果的である。
【００２３】
本発明の第７の光増幅装置は、第４の光増幅装置の後段をｎ個の光増幅部で構成することにより増幅率を高めることを特徴とする。
【００２４】
第７の光増幅装置の後段の出力光が所定のパワーとなるため、後段の光増幅部の励起光パワーは一意的に決定しても良く、固定化することが可能となる。
【００２５】
本発明の第８の光増幅装置は、後段を、励起光の入射によって入力光を増幅する縦続接続したｎ個の光増幅媒体と、ｎ個の光増幅媒体の各々への励起光を発生するｎ個の光源と、ｎ個の光増幅媒体の各々への励起光のパワーを、α₁，α₂，…，α_nを予め定めた定数及びＰ_pを基準励起光パワーとして、縦続の順にα₁Ｐ_p，α₂Ｐ_p，…，α_nＰ_pとしたとき、これらのｎ個の励起光のパワーを制御する励起光制御部とを有し、当該励起光制御部は、入力光を構成する波長の間の利得偏差が一定の状態での、最終段の光増幅媒体の出力光パワーと基準励起光パワーＰ_pの関係を収納した特性情報テーブルと、所定の出力光パワーの値を特性情報テーブルに照合して引き出した基準励起光Ｐ_pのパワーの値を用いてｎ個の光源を制御し、ｎ個の光源の各励起光のパワーを上記引き出した基準励起光Ｐ_pに上記定数を乗じたパワーにする光源制御部を備えた光増幅部とすることを特徴とする。
【００２６】
本発明の上述の各光増幅装置は、入力光パワーや温度の変化に対して利得の波長依存性を小さく抑えることができる他、特性情報テーブルは例えば半導体集積回路によるＲＯＭ（Read Only Memory）によって実現可能であり、また制御部も半導体集積回路によるプロセッサによって実現可能であり、従って、消費電力が小さくかつ部品数の少ない簡易な構成とすることができる。
【００２７】
【発明の実施の形態】
以下、本発明に係る光増幅装置を図面に示した発明の実施の形態を参照して更に詳細に説明する。なお、図３、図４及び図７〜図１３における同一の記号は、同一物又は類似物を表示するものとする。
【００２８】
まず、本発明によって明らかにした希土類添加ファイバの特性について図１を用いて説明する。図１ａは、利得偏差が最小となる励起条件で、幾つかの入力光パワーと温度を変えた場合の実験データから、横軸に励起光パワー（後励起パワー）を縦軸に出力光パワー（ＥＤＦ出力パワー）を取ってプロットしたグラフである。ここで、利得偏差は、増幅されたＷＤＭ信号光において、波長毎に異なる利得を呈するときの最大の信号光利得と最小の信号光利得との差を云うこととする。
【００２９】
実験には、希土類添加ファイバとしてＥＤＦ（エルビウム添加ファイバ）を用いた。ＥＤＦは、エルビウム濃度が４００ｐｐｍで、共添加物としてＡl₂Ｏ₃を加えており、その濃度は１１０００ｐｐｍとした。ＥＤＦの長さは３００ｍとした。ＥＤＦの両側にはＷＤＭ光カプラを介して励起用の半導体レーザダイオードを接続し、双方向から励起を行なった。入力信号光として、波長１５７０，１５７９，１５８９，１５９９ｎｍの４つの光を波長多重した４チャネル（ｃｈ）構成のものを用いた。
【００３０】
入力信号光のパワーを−２８，−２５，−２２ｄＢｍ／ｃｈとし、スペクトルアナライザでスペクトルを常にモニタしながら、増幅された信号光の出力が各波長で同じになるように励起レーザのパワーを調整した。
【００３１】
ＥＤＦの出力スペクトルは、励起光パワーの増加に従い、およそ図２に示すように、左下がり（短波長側信号光の出力小）の状態（図２ｃ）から、左上がり（短波長側信号光の出力大）の状態（図２ａ）へと移行していく。この性質を利用し、スペクトルを見ながら利得偏差が最小となる状態を探し、励起光パワーを調整した。この際、前側励起レーザの励起パワーは１６７ｍＷで固定とし、調整は後側励起レーザの励起パワーに対してのみ行なった。温度は、ＥＤＦを恒温槽に入れて変化させ、０，２５，５０，７０℃の４通りを選んで測定を行なった。
【００３２】
このようにして求めた実験結果を図１ａに示す。図１ａは、入力光パワーと温度を変化させ、利得偏差が最小となる状態（図２ｂ）の出力光パワーと励起光パワーの関係を示したものである。測定点は、図１ａから明らかのように、ほぼ直線上に乗ることが判明した。この直線を最小二乗法によるフィッティングで求めた結果、ｘを励起パワー、ｙを出力光パワーとして、ｙ＝０．７０３７ｘ−１２．２９３の一次関数となった。
【００３３】
なお、励起状態、例えば増幅された自然放出光（Amplified Spontaneous Emission）の影響、或いは出力光のパワーを検出する光検出器の特性等により、出力光パワーと励起光パワーの関係は多少歪んだ曲線になる場合もある。この場合の特性曲線は、ほぼ単調な増加関数となる。
【００３４】
また、この図では利得偏差最小の状態の特性曲線を示しているが、利得偏差が一定の大きさとなる状態の特性曲線もこの特性曲線を上側又は下側に移動して得ることができる。このことから、入力信号光に既に利得偏差がある場合、この偏差と逆の方向の偏差を持つように条件を定めて出力光パワーと励起光パワーの関係を求めると、入力信号光の利得偏差が補正され、光増幅装置から利得偏差最小の出力光を得ることができる。
【００３５】
なお、参考として、利得偏差最小ではなく、利得そのものを一定に制御した場合の励起パワーと出力パワーの関係を図１ｂに示す。この場合、信号光波長は図１ａのときと同じ波長の４チャネルＷＤＭ信号光を用い、入力信号光のパワーを−２８，−２５，−２２，−１９ｄＢｍ／ｃｈとし、温度は０，２５，５０，７０℃の４通りを測定した。入力信号光の全パワーとＥＤＦ出力信号光の全パワーを各々測定し、このときの利得が３０ｄＢで一定になるよう励起パワーを調整した。利得一定制御の場合には、温度が違うと同じ利得を得るために必要な励起パワーが幾分異なるため、入力信号光パワーの大きさに応じてグラフは階段状になることが判明した。
【００３６】
本発明は、図１ａに示した特性を利用することにより、入力光パワー及び温度が変化しても利得偏差が最小で一定となる状態を実現するものである。
【００３７】
本発明の光増幅装置の第１の発明の実施の形態を図３に示す。本発明の実施の形態は、入力ポート１０から入力されたＷＤＭ信号光に励起光を加えるＷＤＭ光カプラ３０と、カプラ３０からのＷＤＭ信号光を増幅する希土類添加ファイバ２０と、励起光を発する光源である励起レーザダイオード４０及びその励起光パワーを検出する光検出器６０を備えた励起部５０と、希土類添加ファイバ２０の出力光の大部分を出力ポート１１に出力し、一部分を分離して取り出すタップカプラ１００と、タップカプラ１００からの分離出力光を入力して希土類添加ファイバ２０の出力光パワーを検出する光検出部１１０と、光検出器６０及び光検出器１１０の検出結果を入力して励起レーザダイオード４０の励起光パワーを制御する励起光制御部７０とによって構成される。
【００３８】
励起レーザダイオード４０は多くの場合、ファブリペロー共振器を伴って構成され、共振器の一方の端部から出射するレーザ光がカプラ３０へ供給される励起光となり、他方の端部から出射するレーザ光が光検出器６０に与えられる。それにより、光検出器６０は、励起レーザダイオード４０のレーザパワーの一部を取り込み、レーザ光パワーに応じた大きさの電流を励起光パワーのモニタ量（検出結果）として出力する。この励起光パワーのモニタ量が励起光制御部７０へ入力される。同様に、光検出器１１０もタップカプラ１００からの分離出力光を取り込み、光パワーに応じた大きさの電流を出力ポート１１へ送られる出力光パワーのモニタ量として出力する。この出力光パワーのモニタ量が励起光制御部７０へ入力される。
【００３９】
励起光制御部７０は、特性情報テーブル８０と励起レーザダイオード４０への駆動信号を生成する制御処理部９０からなる。特性情報テーブル８０は、希土類添加ファイバ２０の利得偏差最小の状態での出力光パワーと励起光パワーの関係の測定結果から得た上記の１次関数を収納したテーブルである。また、特性情報テーブル８０は、光検出部１１０が検出した出力光パワーのモニタ量を入力して当該モニタ量に対応する励起光パワーの値を引き出す。制御処理部９０は、特性情報テーブル８０からの励起光パワーの値と光検出部６０からのモニタ量を入力して両者を比較し、両者に差がある場合に、励起レーザダイオード４０の光出力を特性情報テーブル８０によって引き出された励起光パワーにする駆動信号を生成する。
【００４０】
光増幅媒体である希土類添加ファイバ２０としてＥＤＦを使用した。そして、ＥＤＦの吸収係数が大きい０．９８μｍ帯又は１．４８μｍ帯の発振波長を持つ半導体レーザダイオードを励起レーザダイオード４０として用いた。
【００４１】
なお、図３の構成では、ＷＤＭカプラ３０がＥＤＦ２０の入力端に接続された前方向励起を採用した。ここで、幾つかの励起方法を図４に示す。図４ａは前方向励起、図４ｂはＷＤＭカプラ３１（励起レーザダイオード４１が接続される）がＥＤＦ２０の出力端に接続された後方向励起、図４ｃはＷＤＭカプラ３０，３１がＥＤＦ２０の両端に接続された双方向励起を示している。本発明の実施の形態は、前方向励起に限らず、後方向励起及び双方向励起のいずれも採用可能である。
【００４２】
ここで、特性情報テーブル８０を用いて励起光パワーを決定する手順について図５を用いて説明する。図５では、四角でプロットした点を結んだ直線が特性曲線を示している。一方、丸で示した点は、光検出器６０，１１０のモニタ量によって示されるそれぞれ励起光及び出力光の光パワーの実際の値をプロットした点である。また、直線上の星印は、入力光パワー及び温度によって決定される所望の利得偏差が最小となる状態（制御の目標点、即ち正解値）を示している。
【００４３】
今、図５で示したように、実際の値が特性曲線より下側にあるとする（図中Ａ点）。そこで、励起レーザダイオード４０の駆動電流の大きさを変え、励起光パワーを出力光パワーに対応する特性曲線上の点までシフトさせる（図中Ｂ点）。しかし、このＢ点での励起光パワーの値が、正解（図中の星印）まで達していない場合には、励起光パワーをシフトしたことで得られる実際の値は、特性曲線より下側の点（図中Ｃ点）となる。このように、出力光パワーの検出結果を使って特性曲線から励起光パワーを順次決定し、図中星印に示した制御の目標点まで繰り返し励起光パワーを制御していく。
【００４４】
制御の収束については、図５の丸で示した、励起光及び出力光の光パワーの実際の値から特性曲線を使って計算によって求めた目標とする励起光パワーと励起光パワーの実際の値との差が一定の範囲内になることを収束の条件とすることができる。収束の条件は、その他に、特性曲線を使って出力光パワーの実際の値から求めた励起光パワーと励起光パワーの実際の値との差、即ち、制御処理部９０の比較結果が一定の範囲内になるまでとすることができる。更にその他に、図５の丸で示した点の特性曲線までの距離を求め、その距離の大きさが一定の範囲内になるまでを収束条件とすることができる。収束条件に達した制御を経て、利得偏差最小の状態で増幅された出力信号光が出力ポート１１から送出される。
【００４５】
なお、図５では励起光パワーの増加分及び減少分が特性曲線上の同じＥＤＦ出力パワーとなる点に向かうよう描いてあるが（図中、水平な矢印）、このように増加分および減少分を決定するには駆動電流と励起光パワーの関係をあらかじめ知っておく必要がある。しかし、本発明による制御方法を実現するためには、励起光パワーの増加分および減少分の決定法について任意性を持たせることが可能である。例えば、励起光レーザダイオードの駆動電流の変化分を測定された励起光パワーの値と特性情報テーブル８０によって得られた特性曲線上の励起光パワーの値との差に適当な比例係数を乗じるという方法を採用することができる。この場合、比例係数については、なるべく大きな値でかつ制御において大きな振動が生じない、言い換えれば制御の度に特性曲線上の上側、下側の領域に移り変わることがあまり生じない範囲であることが望ましい。
【００４６】
このように励起レーザダイオード駆動電流の変化分を実際の測定量と理想的な値との差分に比例した量で決めるという方法は、簡易な制御系の実現という観点で幾つか長所がある。この方法では励起レーザダイオード駆動電流と励起光パワーの関係を厳密に知る必要がないため、制御アルゴリズムが簡単となる。また、温度或いは入力信号光パワーが急に変化した場合、実際のＥＤＦ出力パワー測定値と特性曲線上の理想的なＥＤＦ出力パワーの差が大きいときは駆動電流の変化分も大きくすぐに特性曲線上の理想的な点に近づけようとするが、ＥＤＦ出力パワー測定値が特性曲線上の理想的な点に十分近づいた場合には駆動電流の変化分が小さくなるので、制御により大きな振動が生じることなく安定に収束した状態を維持することができる。
【００４７】
以上述べた制御方法のフローチャートを図６に示す。まず、光検出器６０によって励起レーザダイオード４０が発振する励起光パワーを測定する。次に、光検出器１１０により光増幅媒体２０の出力光パワーを測定する。この測定した出力光パワーを特性曲線にあてはめ特性曲線上の励起光パワーを計算する。そして、先に測定した励起光パワーと特性曲線上の励起光パワーとの差を求め、その値だけ励起光パワーを変化させる。このとき、測定した励起光パワーと特性曲線上の励起光パワーとの差があらかじめ定めた一定範囲内に収束すれば制御を終了し、一定範囲内に収束しなければ励起光パワーを測定し、制御を繰り返し行なう。
【００４８】
なお、図５及び図６において、出力光パワーがＣ点に達してから再び励起光パワーをその出力光パワーに対応する特性曲線上の点までシフトさせる繰り返し動作を示したが、光増幅装置の各部の動作によっては、励起光パワーがＡ点から下がっていくのに従って出力光パワーが変化し、その変化する出力光パワーに応じて刻々と変化する励起光パワーの値が特性情報テーブルから引き出される場合があり、その場合の制御動作では、実際の値は、図５のＡ点から星印に向かって曲線を描きながら連続的に変化する。本発明は、云うまでもなくそのような動作を起こす励起光制御部の採用が可能である。
【００４９】
要するに、本発明の光増幅装置の励起光制御部は、入力光を構成する波長の間の利得偏差が一定の状態での、光増幅媒体の出力光パワーと励起光パワーとの関係を収納した特性情報テーブルと、光増幅媒体が増幅して得た出力光のパワーの値を特性情報テーブルに照合して引き出した励起光のパワーの値を用いて光源を制御し、光源の励起光のパワーを上記引き出した励起光のパワーにする光源制御部を備えていればよい。
【００５０】
以上のようにして利得偏差最小即ち利得の波長依存性を最小に抑えた状態で増幅を行なう本発明の実施の形態において、励起光制御部７０は、半導体集積回路によるメモリ及びＣＰＵ（Central Processor Unit）を用いたデジタル回路で構成することが可能である。それによって光増幅装置を、ペルチエ素子やサーミスタを用いた従来の光増幅装置に比べて消費電力が小さくかつ部品数の少ない簡易な構成のものとすることができた。なお、特性曲線が線形関数のような簡単な関係で記述される場合には励起光制御部７０をアナログ回路で構成し、制御速度を向上させることが可能である。
【００５１】
次に、上記の発明に実施の形態の光増幅装置の出力側に、出力光のパワーレベルに応じて減衰量が制御される減衰量が可変の光減衰器（以下「可変光減衰器」という）を設けた第２の発明の実施の形態を図７に示す。図７において、２００は可変光減衰器、１０１は、可変光減衰器２００の出力光の大部分を出力ポート１１に送り出し、一部分を分離して取り出すタップカプラ、１１１は、タップカプラ１０１からの分離出力光を検出する光検出器、２１０は、光検出器１１１の検出結果を受けて可変光減衰器２００の減衰量を制御する減衰量制御部である。
【００５２】
更に、第２の実施の形態においては、特に、入力ポート１０とカプラ３０の間に光アイソレータ１２０を設け、タップカプラ１００と可変光減衰器２００の間に光アイソレータ１２１を設けた。これは、各光部品で反射された光が、伝送路或いはＥＤＦ２０内に入り込むことで伝送特性或いは増幅特性が劣化することを防ぐためのものである。
【００５３】
光検出器１１１は、タップカプラ１０１からの分離出力光を取り込み、分離出力光に対応した大きさの電流を出力ポート１１への出力光パワーのモニタ量として出力する。減衰量制御部２１０は、このモニタ量を受け、出力ポート１１への出力光パワーが所定の値となるように可変光減衰器２００の減衰量を制御する。これにより、入力ポート１０への入力光のパワーレベルが変動して可変光減衰器２００に入力するＥＤＦ２０の出力光のパワーレベルが変動しても、出力ポート１１への出力光は所定の値で一定のパワーレベルとなる。
【００５４】
本発明の実施の形態により、利得の波長依存性を最小に抑えた状態で増幅を行ない、かつ、入力光のパワーレベルが変動しても出力光が所定のパワーレベルで一定となる光増幅装置を得ることができる。
【００５５】
光減衰器の減衰量を光増幅媒体２０の光出力パワーの検出結果によって制御するようにした第３の発明の実施の形態を図８に示す。図７の構成と比べ、タップカプラ１０１とフォトディテクタ１１１が省かれる。減衰量制御部２１０は、光検出器１１０からのモニタ量を受け、出力ポート１１への出力光パワーが所定の値で一定となるように可変光減衰器２００の減衰量を制御する。即ち、可変光減衰器２００は、その入力光パワーに比例した光減衰量が与えられることによって光増幅装置全体として出力一定制御を実現する。
【００５６】
次に、本発明の利得偏差を最小にする励起光制御を用いて高出力の光増幅装置を実現するための方法について説明する。図１に示した単体の光増幅装置を光増幅部と云うこととすると、高出力の光増幅装置は、複数個の光増幅部を多段縦続接続することによって実現することができる。各光増幅部には本発明による励起光制御が適用される。また、高出力の光増幅装置には、出力光のパワーレベルを一定にするための減衰量制御を受ける可変光減衰器が採用される。
【００５７】
このとき、可変光減衰器は、複数の光増幅部に対し少なくとも１個あれば出力光のパワーレベル一定を実現することができる。なお、励起効率を考えると、可変光減衰器の位置は、多段縦続接続の最終段の光増幅部よりも前にあることが望ましい。可変光減衰器を最終段の光増幅部の出力側に配置すると、可変光減衰器には制御に用いる減衰量があるので、その分光増幅部の出力光パワーを大きくする必要があるからである。即ち、光増幅媒体は、大きな励起光パワーを必要とする。しかし、可変光減衰器を最終段よりも前に配置する場合は、その後段で増幅が行なわれるので、可変光減衰器の直前にある光増幅部の出力光パワーは低く設定することができる。従って、可変光減衰器直前の光増幅部の光増幅媒体は、大きな励起光パワーを必要としない。このような可変光減衰器の配置により、最終段の光増幅部での無駄となる励起光パワーを用意することが避けられる。
【００５８】
また、微弱な低パワーの入力光を増幅する場合は、光増幅装置の雑音指数の観点から、入力ポートと光増幅部の間に光損失を持つものを置くことを避けることが望ましい。
【００５９】
従って、高出力でかつ低雑音指数の光増幅装置を実現するためには、可変光減衰器の前後に少なくとも１台の光増幅部が配置されることが望ましい。
【００６０】
このような高出力かつ低雑音指数を備えるための構成を採用した第４の発明の実施の形態を図９に示す。図９の光増幅装置は、光増幅部２段の構成であり、その中間に可変光減衰器２００が配置される。図９において、入力ポート１０は光アイソレータ１２０に接続され、続いて第１の発明の実施の形態の説明で述べた光増幅装置が第１の光増幅部として配置される。この第１の光増幅部で増幅された信号光は、光アイソレータ１２１を介して可変光減衰器２００に出力される。
【００６１】
可変光減衰器２００の出力側に第１の発明の実施の形態の説明で述べた光増幅装置が第２の光増幅部として配置される。ただし、第２の光増幅部では、後方励起が採用される。第２の光増幅部は、可変光減衰器２００の出力光を入力する希土類添加ファイバ２１と、希土類添加ファイバ２１に励起光を与えるＷＤＭ光カプラ３１と、励起光を発する光源である励起レーザダイオード４１及びその励起光パワーを検出する光検出器６１を備えた励起部５１と、ＷＤＭ光カプラ３１の出力光を受ける光アイソレータ１２２と、光アイソレータ１２２の出力光の大部分を出力ポート１１に出力し、一部分を分離して取り出すタップカプラ１０１と、タップカプラ１０１からの分離出力光を入力して希土類添加ファイバ２１の出力光パワーを検出する光検出部１１１と、光検出器６１及び光検出器１１１の検出結果を入力して励起レーザダイオード４１の励起光パワーを制御する励起光制御部７１とによって構成される。更に励起光制御部７１は、特性情報テーブル８１と励起レーザダイオード４１への駆動信号を生成する制御処理部９１からなる。本光増幅装置で増幅された信号光は出力ポート１１を経て伝送路に出力される。
【００６２】
可変光減衰器２００の減衰量を制御する減衰量制御部２１０に、第２の光増幅部の光検出器１１１の出力するモニタ量が入力される。減衰量制御部２１０は、出力ポート１１の出力光パワーが所定の値で一定となるように可変光減衰器２００の減衰量を制御する。
【００６３】
ところで、光伝送システムによっては、伝送路に送出するＷＤＭ信号光の光出力のチャネル当たりのパワーが定められている場合がある。この場合は、チャネル数をｍ、チャネル当たりのパワーをＰoとすると、伝送路への光出力のパワーはｍＰoとなる。
【００６４】
このような光伝送システムに用いる光増幅装置にＷＤＭ信号光のチャネル数即ち信号光数についての情報を得られる仕組みがある場合には、図９に示した光増幅装置において、光検出器１１１から励起光制御部７１へのモニタ量の提供を省略し、そのための配線を省略することができる。そのような構成を採用した第５の発明の実施の形態を図１０に示す。信号光数情報は、第２の光増幅部における励起光制御部７１の特性情報テーブル８１に与えられる。これまでの発明の実施の形態では、励起光制御部７１は、モニタされた出力光パワーによって励起光パワーを決定していたが、本発明の実施の形態では、出力光パワーを信号光数情報から一意に決定することができるため、励起光制御部７１は、信号光数情報によって励起光パワーを決定する。
【００６５】
即ち、励起光制御部７１は、信号光数情報から所定の出力光パワーの値を計算する計算部（図示せず）を有し、計算値を特性情報テーブル８１に与える。特性情報テーブル８１は、出力光パワーの計算値に対応する励起光パワーの値を引き出す。制御処理部９１は、特性情報テーブル８１からの励起光パワーの値と光検出部６１からのモニタ量を入力して両者を比較し、両者に差がある場合に、励起レーザダイオード４１の光出力を特性情報テーブル８１によって引き出された励起光パワーにするための駆動信号を生成する。
【００６６】
このようにして、利得偏差が最小で一定の状態が実現し、続いて減衰量制御部２１０が光検出器１１１からのモニタ量を受け、光増幅装置の出力光が所定のパワーで一定となるように可変光減衰器２００を制御する。
【００６７】
信号光数を得る手段としては、光増幅装置に保守者が直接設定を行なう方法を採用することができるが、光増幅装置内部にチャネルカウンタ部を備え、当該カウンタ部で自律的に信号光数をカウントする方法も採用可能である。チャネルカウンタ部は、簡単には光増幅装置の入力信号光を波長軸上にスキャンし、そのピーク数をカウントすることによって実現することができる。また、信号光数を得る更に別の手段として、信号光とは別の波長の監視制御光を伝送路上に送信し、その監視制御光に信号光数情報を乗せて伝達する方法を採用可能である。この方法を実行するために、励起光制御部７０は、監視制御光を受ける監視制御光インタフェース部（図示せず）を備え、監視制御光インタフェース部から信号光数情報を得る。
【００６８】
ところで、図１０の構成において、システム上雑音指数の劣化をさほど気にしなくてもよい場合には、第１の光増幅部を省略することが可能になる。そのような前段に可変光減衰器を配置した１個の増幅器による第６の発明の実施の形態を図１１に示す。
【００６９】
以上は、２段又は１段の光増幅部による構成の実施形態であるが、構成を三段以上とした第７の発明の実施の形態を図１２に示す。本発明の実施の形態は、可変光減衰器２００の前に光増幅部が１段配置され、可変光減衰器２００の後に光増幅部がｎ段縦続接続される。図１２において、ｎ個のＥＤＦ２１−１〜２１−ｎは、それぞれＷＤＭカプラ３１−１〜３１−ｎを介して複数の励起部５１−１〜５１−ｎが接続され、更に各々の励起光制御部７１−１，…，７１−ｎによって上述の発明の実施の形態と同様の制御を受け、利得偏差最小の状態が実現される。減衰量制御部２１０は、最終段のＥＤＦ２１−ｎの出力光パワーを検出する光検出器１１１−ｎが出力するモニタ値を入力して可変光減衰器２００の減衰量を制御し、光増幅装置全体として出力一定制御を行なう。本発明の実施の形態により、高い光パワーを出力する光増幅装置を実現することができる。
【００７０】
励起光制御部の特性情報テーブルをｎ段の光増幅部で共通化して単一化した第８の発明の実施の形態を図１３に示す。本発明の実施の形態では、まず、α₁，α₂，…，α_nを予め定めた定数として、ＥＤＦ２１−１〜２１−ｎへの励起光パワーを順にα₁Ｐ_p，α₂Ｐ_p，…，α_nＰ_pとし、ｎ段の光増幅部を纏めて１個の光増幅部とみなし、その光増幅部の出力光パワー（即ちｎ段目光増幅部の出力光パワー）と上記の基準励起光パワーＰ_pとの関係の利得偏差が最小となる特性曲線を求め、特性情報テーブル８１に格納しておく。励起光制御部９１は、計算部（図示せず）を使って信号光数情報から所定の出力光パワーを算出し、その値を特性情報テーブル８１に与える。特性情報テーブル８１は、所定の出力光パワーの値に対応する基準励起光パワーＰ_pを取り出す。制御処理部９１は、基準励起光パワーＰ_pから励起レーザダイオード４１−１〜４１−ｎの励起光パワーがα₁Ｐ_p，α₂Ｐ_p，…，α_nＰ_pとなるように、各励起レーザダイオードへの駆動信号を生成する。本発明の実施の形態により、構成が簡単な多段縦続接続の光増幅装置を実現することができる。
【００７１】
なお、α₁＝α₂＝…＝α_nとして、励起レーザダイオード４１−１〜４１−ｎの各々の出力パワーが等しくなるようにして励起光パワーを制御することが可能である。光増幅装置の構成がより簡単になる。
【００７２】
【発明の効果】
本発明によれば、入力光パワー及び環境温度が変化しても波長多重伝送の各信号光の利得偏差を抑制して増幅する光増幅装置を実現することができる。従って、温度安定化のための部品や温度測定用の部品及びそれらへの制御装置が不要となるため、消費電力が少なく増幅特性に優れた簡易で安価な波長多重光増幅装置を実現することができる。そして、本発明の光増幅装置を用いることで、伝送特性の優れた簡易で安価な光通信システムを構築することができる。
【図面の簡単な説明】
【図１】本発明によって明らかにした希土類添加ファイバの性質を説明するための図。
【図２】光増幅装置の励起光パワーと出力光パワーの波長依存性を示す図。
【図３】本発明に係る光増幅装置の第１の発明の実施の形態を説明するための構成図。
【図４】光増幅装置における励起方法を説明するための構成図。
【図５】特性情報テーブルを用いて励起光パワーを決定する手順を説明するための図。
【図６】特性情報テーブルを用いた励起光制御の方法を説明するためのフローチャート図。
【図７】本発明に係る光増幅装置の第２の発明の実施の形態を説明するための構成図。
【図８】本発明に係る光増幅装置の第３の発明の実施の形態を説明するための構成図。
【図９】本発明に係る光増幅装置の第４の発明の実施の形態を説明するための構成図。
【図１０】本発明に係る光増幅装置の第５の発明の実施の形態を説明するための構成図。
【図１１】本発明に係る光増幅装置の第６の発明の実施の形態を説明するための構成図。
【図１２】本発明に係る光増幅装置の第７の発明の実施の形態を説明するための構成図。
【図１３】本発明に係る光増幅装置の第８の発明の実施の形態を説明するための構成図。
【符号の説明】
１０…入力ポート、１１…出力ポート、２０，２１…希土類添加ファイバ、３０，３１…ＷＤＭ光カプラ、４０，４１…励起レーザダイオード、５０，５１…励起部、６０，６１，１１０〜１１２…光検出器、７０，７１…励起光制御部、８０，８１…特性情報テーブル、９０，９１…制御処理部、１００〜１０２…タップカプラ、１２０〜１２２…光アイソレータ、２００…可変光減衰器、２１０…減衰量制御部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical amplifying apparatus used in an optical communication system, and more particularly to an optical amplifying apparatus suitable for being applied to a system employing an optical transmission method based on wavelength multiplexing.
[0002]
[Prior art]
In recent years, research and practical application of an optical transmission system using an optical amplifying device as a repeater have been active. In particular, in order to support multimedia services centering on the Internet, it is effective to increase the capacity by WDM (Wavelength Division Multiplex) that multiplexes a plurality of signal lights having different wavelengths. In an optical communication system using this WDM technology, an optical repeater amplifier that amplifies all signal lights collectively in order to increase the transmission distance plays an extremely important role.
[0003]
As an optical amplifying medium for constructing this optical amplifying device, an optical fiber doped with rare earth is effective, and research and practical application are currently underway. In particular, an erbium-doped fiber (hereinafter referred to as “EDF (Erbium-Doped Fiber)”) is widely used in optical fiber communication systems because it has an amplifying function in a wide range of wavelengths where the optical fiber has low loss.
[0004]
In order to give the optical amplification medium an amplification effect in the signal light wavelength band, excitation light having a shorter wavelength than the signal light is incident on the optical amplification medium together with the signal light. A WDM optical coupler is connected to the end of the optical amplifying medium so that the signal light and the pumping light are efficiently incident on the optical amplifying medium.
[0005]
However, when rare earth-doped optical fiber amplifies WDM signal light in a lump, the region where the gain does not have wavelength dependence is narrow, and wavelength dependence occurs due to changes in input signal light power only by limiting the wavelength range. End up. As this solution, by measuring the input power and output power of the optical amplifying medium, and by adjusting the power of the pumping light so that the average gain obtained from the measured value is constant (Automatic Gain Control: AGC), It is known that the wavelength dependence of gain at different input powers can be suppressed. In the optical amplifying apparatus using this method, a constant output control using a variable optical attenuator is further employed.
[0006]
However, in an actual optical amplifying device, the gain characteristic changes depending on the temperature in addition to the input power. For this reason, even if the optical amplifying apparatus is designed so that the wavelength dependence of gain becomes small at a certain temperature, it is inevitable that wavelength dependence will occur due to temperature change during use only by control by AGC. .
[0007]
In order to solve this problem, several techniques for maintaining the gain of the optical amplifying device uniform in wavelength are known. For example, according to the technique disclosed in Japanese Patent Laid-Open No. 4-11794, the temperature of the optical amplifying medium is controlled to be constant using a temperature control device such as a Peltier element. Thereby, the gain of the optical amplifying device becomes uniform in wavelength. Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. 10-335722, the temperature dependence is measured using a thermistor, and the wavelength dependence of the gain is corrected by controlling the characteristics of the light transmission element according to the temperature. .
[0008]
[Problems to be solved by the invention]
However, the conventional example has the following problems. For example, in a method using a temperature control device such as a Peltier element, it is unavoidable that the power consumption increases, and the apparatus becomes complicated and large in order to emit heat generated by operating the Peltier element. Further, in the method of correcting the wavelength dependence of gain using a thermistor and a light transmissive element, it is difficult to realize a light transmissive element for sufficiently correcting the wavelength dependence of EDF gain caused by a change in input power or temperature. . Further, since the correction is made by adding the temperature to the parameter, it is inevitable that the number of parts increases and the control method becomes complicated.
[0009]
The object of the present invention is to solve the above-mentioned problems of the prior art and to prevent the wavelength dependence of the gain from occurring even if the input optical power and temperature are changed. An object of the present invention is to provide an optical amplifying device having a small number of simple configurations.
[0010]
[Means for Solving the Problems]
From the results of experiments on rare earth-doped fibers, the present inventor has shown that the output in a state where the wavelength dependence of gain is constant, that is, the gain deviation between wavelengths is constant, when the input optical power and temperature are variously changed. The characteristic curve representing the relationship between optical power and pumping light power is a simple monotonically increasing function or linear function, and the output light power and pumping light power are kept on the characteristic curve based on these functions. Then, it has been found that a gain characteristic can be obtained in which the wavelength dependence does not change even when the input optical power and temperature change. Therefore, if a characteristic curve with no gain deviation is employed and the output light power and the pumping light power are on the characteristic curve, an optical amplifier without gain deviation can be obtained. This will be described in detail later. If there is a gain deviation in the input light, the characteristic curve of the opposite deviation is adopted, and if the output light power and the pumping light power are on the characteristic curve, the output from the optical amplifier has no gain deviation. Light can be obtained.
The “state where the gain deviation is constant” means, for example, the state shown in FIG. Here, the value of the gain deviation is shown in FIG. (a) As shown in FIG. 2, when a negative value is taken (for example, when the deviation is defined by (maximum wavelength gain) − (minimum wavelength gain), the same applies hereinafter) and FIG. (c) In some cases, a positive value may be taken. FIG. ( b ) If (a) , (c) In this special case, the gain deviation is constant or zero.
Further, the “curve” of the above-described characteristic curve includes a straight line.
[0011]
The present invention has been made based on such knowledge. That is, the object of the present invention is to provide a characteristic information table that stores a characteristic curve that represents the relationship between the pumping light power and output light power of the optical amplifying medium when the gain deviation of each wavelength multiplexed signal light is constant. In addition, it is possible to effectively solve the problem by including a pumping light control unit that controls the pumping light power so that the output light power and the pumping light power of the optical amplification medium follow the relationship given by the characteristic curve. . By adopting such a means, the relationship between the output light power and the pump light power according to the characteristic curve is maintained, and even if the input light power and the environmental temperature change, a gain characteristic having no wavelength dependency can be obtained. It is.
[0012]
Specifically, a first optical amplifying device of the present invention includes an optical amplification medium that amplifies input light by the incidence of excitation light, a light source that generates the excitation light, and an excitation light control unit that controls the power of the excitation light. The pumping light control unit stores the relationship between the output light power of the optical amplifying medium and the pumping light power when the gain deviation between the wavelengths constituting the input light is constant. The light source is controlled using the information table and the power value of the pumping light extracted by collating the power value of the output light obtained by amplification by the optical amplifying medium with the characteristic information table. It has a light source control unit for making the power of the extracted excitation light.
[0013]
Even if the input light is not wavelength-dependent, its power may change and arrive. In such a case, it is effective to employ a configuration in which an optical attenuator having a variable attenuation amount is arranged in the optical amplifying device and the attenuation amount of the optical attenuator is controlled so that the output optical power becomes constant. Become.
[0014]
The second optical amplifying device of the present invention is an embodiment in which the output optical power is made constant, and further the attenuation amount variable light that is output to the first optical amplifying device by further attenuating the output light of the optical amplification medium. An attenuator, and an attenuation amount control unit that controls the attenuation amount of the optical attenuator so that the output light of the optical attenuator becomes a predetermined power using the detection result of the output optical power of the optical attenuator. Features.
[0015]
The third optical amplifying device of the present invention is another embodiment in which the output optical power is made constant, and the attenuation amount variable for outputting the output light of the optical amplifying medium by further attenuating to the first optical amplifying device. And an attenuation amount control unit for controlling the attenuation amount of the optical attenuator so that the output light of the optical attenuator becomes a predetermined power using the detection result of the output optical power of the optical amplifying medium. It is characterized by.
[0016]
In the second and third configurations, the output optical power of the optical amplifying device is increased by the attenuation amount of the optical attenuator. When the optical amplifying device drives an optical fiber, the output light power is required to be large, and the power consumption is also large. Therefore, the attenuation amount may be a burden. In such a case, it is effective that the optical amplifying device is composed of two optical amplifying devices at the front stage and the rear stage, and an optical attenuator is arranged between them. The pre-stage optical amplifying device has a light restriction on the output optical power, and the amount of attenuation is not a burden.
[0017]
The fourth optical amplifying device according to the present invention is an embodiment having such a two-stage configuration of the former stage and the latter stage. Optically using the detection result of the output light power of the rear-stage optical amplifying unit so that the output light of the rear-stage optical amplifying unit becomes a predetermined power by being connected in cascade through an optical attenuator. An attenuation amount control unit for controlling the attenuation amount of the attenuator is connected to the output side of the subsequent optical amplification unit.
[0018]
Since the output light has a predetermined power in the fourth optical amplifying device, the pumping light power of the subsequent optical amplifying unit may be uniquely determined and can be fixed.
[0019]
The fifth optical amplifying device of the present invention sets the pumping light power value extracted from the characteristic information table of the subsequent optical amplifying unit to the pumping light power value corresponding to the predetermined output light power value. The pumping light power of the latter optical amplifying unit is fixed.
[0020]
When the power of the input light is relatively large, it is possible to omit the previous amplification unit in the fifth optical amplification device.
[0021]
A sixth optical amplifying device according to the present invention is configured by an optical attenuator and a subsequent optical amplifying unit in the fifth optical amplifying device.
[0022]
In addition, in an optical transmission system, there is a case where a high amplification factor is required (for example, a case where an optical fiber relay interval is set to be long). In such a case, it is effective to employ a configuration in which a plurality of optical amplifying devices are connected in cascade.
[0023]
The seventh optical amplifying device of the present invention is characterized in that the amplification factor is increased by configuring the latter stage of the fourth optical amplifying device with n optical amplifying units.
[0024]
Since the output light at the subsequent stage of the seventh optical amplifying device has a predetermined power, the pumping light power of the optical amplifier at the subsequent stage may be uniquely determined and can be fixed.
[0025]
In the eighth optical amplifying device of the present invention, the subsequent stage generates n light amplifying media connected in cascade to amplify the input light by the incidence of the pumping light, and pumping light to each of the n light amplifying media. The power of pumping light to each of the n light sources and the n optical amplification media is expressed as α₁, Α₂, ..., α_nIs a predetermined constant and P_pAs the reference pumping light power,₁P_p, Α₂P_p, ..., α_nP_pThen, the pumping light control unit that controls the power of these n pumping light, the pumping light control unit, in a state where the gain deviation between the wavelengths constituting the input light is constant, Output optical power and reference pumping light power P of the final stage optical amplifying medium_pAnd a reference pumping light P extracted by collating a predetermined output light power value with the characteristic information table._pN light sources are controlled using the power value of the reference pumping light P, and the power of each pumping light of the n light sources is extracted from the above._pThe optical amplification unit includes a light source control unit that multiplies the power by the constant.
[0026]
Each of the above-described optical amplifying devices of the present invention can suppress the wavelength dependence of gain with respect to changes in input optical power and temperature, and the characteristic information table is, for example, a ROM (Read Only Memory) by a semiconductor integrated circuit. The control unit can also be realized by a processor using a semiconductor integrated circuit. Therefore, the power consumption can be reduced and the number of components can be reduced.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the optical amplifying device according to the present invention will be described in more detail with reference to the embodiments of the invention shown in the drawings. 3, 4, and 7 to 13 indicate the same or similar items.
[0028]
First, the characteristics of the rare earth doped fiber clarified by the present invention will be described with reference to FIG. FIG. 1a shows that the pump light power (post pump power) is plotted on the horizontal axis and the output light power (vertical pump power) is plotted on the vertical axis based on experimental data when several input optical powers and temperatures are changed under the pumping conditions with the minimum gain deviation. (EDF output power) is a graph plotted. Here, the gain deviation refers to the difference between the maximum signal light gain and the minimum signal light gain when the amplified WDM signal light exhibits different gains for each wavelength.
[0029]
In the experiment, EDF (erbium-doped fiber) was used as a rare earth-doped fiber. EDF has an erbium concentration of 400 ppm and Al as a co-additive.₂O_ThreeThe concentration was 11000 ppm. The length of the EDF was 300 m. Excitation semiconductor laser diodes were connected to both sides of the EDF via WDM optical couplers to perform excitation from both directions. As the input signal light, a four-channel (ch) configuration in which four lights of wavelengths 1570, 1579, 1589, and 1599 nm are wavelength-multiplexed was used.
[0030]
Adjust the power of the pump laser so that the output of the amplified signal light is the same at each wavelength, while the input signal light power is -28, -25, -22 dBm / ch, and the spectrum is constantly monitored by the spectrum analyzer. did.
[0031]
As shown in FIG. 2, the output spectrum of the EDF increases from the state of lower left (short wavelength side signal light output) (FIG. 2c) to the left of short wavelength side signal light as shown in FIG. The state shifts to the state of “large output” (FIG. 2 a). Using this property, the state where the gain deviation was minimized was found while looking at the spectrum, and the pumping light power was adjusted. At this time, the pump power of the front pump laser was fixed at 167 mW, and adjustment was performed only for the pump power of the rear pump laser. The temperature was changed by putting EDF in a constant temperature bath and selecting four kinds of temperatures of 0, 25, 50, and 70 ° C.
[0032]
The experimental results thus obtained are shown in FIG. FIG. 1a shows the relationship between the output light power and the pump light power in a state where the gain deviation is minimized (FIG. 2b) by changing the input light power and temperature. As is apparent from FIG. 1a, the measurement point was found to be on a substantially straight line. As a result of obtaining this straight line by fitting by the method of least squares, it became a linear function of y = 0.7037x-12.293, where x is the excitation power and y is the output light power.
[0033]
Note that the relationship between the output light power and the excitation light power is a slightly distorted curve due to the excitation state, for example, the influence of amplified spontaneous emission (Amplified Spontaneous Emission) or the characteristics of the photodetector that detects the power of the output light. Sometimes it becomes. The characteristic curve in this case is an almost monotonous increasing function.
[0034]
Further, in this figure, a characteristic curve with the minimum gain deviation is shown, but a characteristic curve with a constant gain deviation can be obtained by moving the characteristic curve upward or downward. From this, if there is already a gain deviation in the input signal light, the gain deviation of the input signal light can be determined by setting the condition to have a deviation in the opposite direction to this deviation and determining the relationship between the output light power and the excitation light power. Is corrected, and output light with a minimum gain deviation can be obtained from the optical amplifying device.
[0035]
For reference, FIG. 1b shows the relationship between the excitation power and the output power when the gain itself is controlled to be constant, not the gain deviation minimum. In this case, the signal light wavelength is a 4-channel WDM signal light having the same wavelength as that in FIG. 1a, the input signal light power is −28, −25, −22, −19 dBm / ch, and the temperatures are 0, 25, Four measurements at 50 and 70 ° C. were measured. The total power of the input signal light and the total power of the EDF output signal light were measured, and the excitation power was adjusted so that the gain at this time was constant at 30 dB. In the case of constant gain control, it was found that the pump power required to obtain the same gain is somewhat different at different temperatures, so that the graph is stepped depending on the magnitude of the input signal light power.
[0036]
The present invention realizes a state in which the gain deviation is minimum and constant even when the input optical power and temperature are changed by utilizing the characteristics shown in FIG. 1a.
[0037]
An embodiment of the first invention of the optical amplifying device of the present invention is shown in FIG. The embodiment of the present invention includes a WDM optical coupler 30 that adds pumping light to WDM signal light input from an input port 10, a rare earth-doped fiber 20 that amplifies the WDM signal light from the coupler 30, and a light source that emits pumping light. Most of the output light from the pumping laser diode 40 and the light detector 60 that detects the pumping light power of the pumping laser diode 40 and the rare earth doped fiber 20 is output to the output port 11, and a part is separated and extracted. The tap coupler 100, the light detection unit 110 that receives the separated output light from the tap coupler 100 and detects the output light power of the rare earth doped fiber 20, and the detection results of the light detector 60 and the light detector 110 are input. The pumping light control unit 70 controls the pumping light power of the pumping laser diode 40.
[0038]
The pump laser diode 40 is often configured with a Fabry-Perot resonator, and laser light emitted from one end of the resonator becomes pump light supplied to the coupler 30, and laser emitted from the other end. Light is provided to the photodetector 60. Thereby, the photodetector 60 takes in a part of the laser power of the excitation laser diode 40 and outputs a current having a magnitude corresponding to the laser light power as a monitoring amount (detection result) of the excitation light power. The monitoring amount of the excitation light power is input to the excitation light control unit 70. Similarly, the photodetector 110 also captures the separated output light from the tap coupler 100 and outputs a current having a magnitude corresponding to the optical power as a monitor amount of the output optical power sent to the output port 11. This output light power monitor amount is input to the pumping light controller 70.
[0039]
The excitation light control unit 70 includes a characteristic information table 80 and a control processing unit 90 that generates a drive signal for the excitation laser diode 40. The characteristic information table 80 is a table that stores the linear function obtained from the measurement result of the relationship between the output light power and the pumping light power when the rare earth doped fiber 20 has the minimum gain deviation. Further, the characteristic information table 80 receives the monitor amount of the output light power detected by the light detection unit 110 and extracts the value of the excitation light power corresponding to the monitor amount. The control processing unit 90 inputs the pumping light power value from the characteristic information table 80 and the monitoring amount from the light detecting unit 60, compares them, and if there is a difference between them, the light output of the pumping laser diode 40 is output. Is generated with the pumping light power extracted by the characteristic information table 80.
[0040]
An EDF was used as the rare earth-doped fiber 20 which is an optical amplification medium. A semiconductor laser diode having an oscillation wavelength in the 0.98 μm band or 1.48 μm band having a large EDF absorption coefficient was used as the excitation laser diode 40.
[0041]
In the configuration of FIG. 3, forward excitation in which the WDM coupler 30 is connected to the input end of the EDF 20 is employed. Here, several excitation methods are shown in FIG. 4a shows forward pumping, FIG. 4b shows backward pumping when the WDM coupler 31 (to which the pumping laser diode 41 is connected) is connected to the output end of the EDF 20, and FIG. 4c shows WDM couplers 30 and 31 connected to both ends of the EDF 20. Shows bidirectional excitation. The embodiment of the present invention is not limited to forward excitation, and can employ both backward excitation and bidirectional excitation.
[0042]
Here, the procedure for determining the pumping light power using the characteristic information table 80 will be described with reference to FIG. In FIG. 5, a straight line connecting points plotted by squares indicates a characteristic curve. On the other hand, the points indicated by circles are points where actual values of the optical powers of the excitation light and the output light indicated by the monitor amounts of the photodetectors 60 and 110 are plotted. A star on the straight line indicates a state (a target point of control, that is, a correct value) in which a desired gain deviation determined by the input optical power and temperature is minimized.
[0043]
As shown in FIG. 5, it is assumed that the actual value is below the characteristic curve (point A in the figure). Therefore, the magnitude of the drive current of the pump laser diode 40 is changed, and the pump light power is shifted to a point on the characteristic curve corresponding to the output light power (point B in the figure). However, when the pump light power value at point B does not reach the correct answer (star in the figure), the actual value obtained by shifting the pump light power is lower than the characteristic curve. (Point C in the figure). In this way, the pumping light power is sequentially determined from the characteristic curve using the detection result of the output light power, and the pumping light power is repeatedly controlled up to the control target point indicated by an asterisk in the figure.
[0044]
Regarding the convergence of the control, the target pumping light power and the actual values of the pumping light power obtained by calculation using the characteristic curve from the actual values of the optical power of the pumping light and the output light shown by circles in FIG. It can be set as a condition for convergence that the difference between is within a certain range. In addition to the convergence condition, the difference between the pump light power obtained from the actual value of the output light power using the characteristic curve and the actual value of the pump light power, that is, the comparison result of the control processing unit 90 is constant. Until it is within range. In addition, the distance to the characteristic curve of the point indicated by a circle in FIG. 5 can be obtained, and the convergence condition can be set until the magnitude of the distance falls within a certain range. Through control that has reached the convergence condition, output signal light amplified with a minimum gain deviation is transmitted from the output port 11.
[0045]
In FIG. 5, the increase and decrease of the pump light power are drawn so as to go to the same EDF output power on the characteristic curve (horizontal arrows in the figure). It is necessary to know in advance the relationship between the drive current and the excitation light power. However, in order to realize the control method according to the present invention, it is possible to give an arbitrary method for determining the increase and decrease of the pumping light power. For example, an appropriate proportionality coefficient is multiplied by the difference between the measured pumping light power value of the pumping laser diode drive current change and the pumping light power value on the characteristic curve obtained from the characteristic information table 80. The method can be adopted. In this case, it is desirable that the proportionality coefficient is as large as possible and does not cause a large vibration in the control. In other words, the proportional coefficient is preferably in a range where the upper and lower regions of the characteristic curve are not frequently changed each time the control is performed. .
[0046]
Thus, the method of determining the amount of change in the excitation laser diode drive current by an amount proportional to the difference between the actual measurement amount and the ideal value has several advantages from the viewpoint of realizing a simple control system. In this method, since it is not necessary to strictly know the relationship between the pumping laser diode driving current and the pumping light power, the control algorithm is simplified. Also, when the temperature or input signal light power changes suddenly, if the difference between the actual measured EDF output power and the ideal EDF output power on the characteristic curve is large, the change in the drive current is also large and the characteristic curve immediately. It tries to approach the ideal point above, but when the measured value of EDF output power is sufficiently close to the ideal point on the characteristic curve, the amount of change in the drive current is small, resulting in large vibrations due to control. It is possible to maintain a stable converged state without any problems.
[0047]
A flowchart of the control method described above is shown in FIG. First, the excitation light power generated by the excitation laser diode 40 is measured by the photodetector 60. Next, the output light power of the optical amplifying medium 20 is measured by the photodetector 110. The measured output light power is applied to the characteristic curve, and the excitation light power on the characteristic curve is calculated. Then, a difference between the pumping light power measured previously and the pumping light power on the characteristic curve is obtained, and the pumping light power is changed by that value. At this time, if the difference between the measured excitation light power and the excitation light power on the characteristic curve converges within a predetermined range, the control is terminated, and if not converged within the certain range, the excitation light power is measured. Repeat the control.
[0048]
In FIGS. 5 and 6, the repeated operation of shifting the pumping light power again to the point on the characteristic curve corresponding to the output light power after the output light power reaches the point C is shown. Depending on the operation of each part, the output light power changes as the pump light power decreases from the point A, and the value of the pump light power that changes momentarily according to the changing output light power is extracted from the characteristic information table. In the control operation in that case, the actual value continuously changes while drawing a curve from the point A in FIG. 5 toward the star. Needless to say, the present invention can employ an excitation light controller that causes such an operation.
[0049]
In short, the pumping light control unit of the optical amplifying device of the present invention stores the relationship between the output light power and the pumping light power of the optical amplifying medium when the gain deviation between the wavelengths constituting the input light is constant. The light source is controlled using the characteristic information table and the power value of the pumping light extracted by collating the power value of the output light obtained by amplification by the optical amplifying medium with the characteristic information table. May be provided with a light source control unit for making the power of the extracted excitation light.
[0050]
In the embodiment of the present invention in which amplification is performed while minimizing gain deviation, that is, the wavelength dependence of gain is minimized as described above, the excitation light control unit 70 includes a memory and a CPU (Central Processor Unit) by a semiconductor integrated circuit. ). As a result, the optical amplifying apparatus has a simple configuration with lower power consumption and fewer parts than the conventional optical amplifying apparatus using a Peltier element or thermistor. When the characteristic curve is described with a simple relationship such as a linear function, the excitation light control unit 70 can be configured with an analog circuit to improve the control speed.
[0051]
Next, on the output side of the optical amplifying device according to the above-described invention, an optical attenuator whose attenuation is controlled according to the power level of the output light (hereinafter referred to as “variable optical attenuator”). FIG. 7 shows an embodiment of the second invention provided with In FIG. 7, reference numeral 200 denotes a variable optical attenuator, 101 denotes a tap coupler that sends most of the output light of the variable optical attenuator 200 to the output port 11 and takes out a part of the output light, and 111 denotes a separation from the tap coupler 101. A photodetector 210 that detects output light is an attenuation control unit that controls the attenuation of the variable optical attenuator 200 based on the detection result of the photodetector 111.
[0052]
Further, in the second embodiment, in particular, the optical isolator 120 is provided between the input port 10 and the coupler 30, and the optical isolator 121 is provided between the tap coupler 100 and the variable optical attenuator 200. This is to prevent the light reflected from each optical component from entering the transmission path or the EDF 20 to deteriorate the transmission characteristics or amplification characteristics.
[0053]
The photodetector 111 takes in the separated output light from the tap coupler 101 and outputs a current having a magnitude corresponding to the separated output light as a monitor amount of the output light power to the output port 11. The attenuation amount control unit 210 receives this monitoring amount, and controls the attenuation amount of the variable optical attenuator 200 so that the output optical power to the output port 11 becomes a predetermined value. Thereby, even if the power level of the input light to the input port 10 fluctuates and the power level of the output light of the EDF 20 input to the variable optical attenuator 200 fluctuates, the output light to the output port 11 has a predetermined value. A constant power level.
[0054]
According to an embodiment of the present invention, an optical amplifying device that performs amplification while minimizing the wavelength dependence of gain, and makes output light constant at a predetermined power level even when the power level of input light fluctuates Can be obtained.
[0055]
FIG. 8 shows an embodiment of the third invention in which the attenuation amount of the optical attenuator is controlled by the detection result of the optical output power of the optical amplifying medium 20. Compared with the configuration of FIG. 7, the tap coupler 101 and the photodetector 111 are omitted. The attenuation amount control unit 210 receives the monitor amount from the photodetector 110 and controls the attenuation amount of the variable optical attenuator 200 so that the output optical power to the output port 11 becomes constant at a predetermined value. That is, the variable optical attenuator 200 realizes constant output control as the entire optical amplifying apparatus by being given an optical attenuation amount proportional to the input optical power.
[0056]
Next, a method for realizing a high-power optical amplifying apparatus using the pumping light control that minimizes the gain deviation of the present invention will be described. If the single optical amplifying device shown in FIG. 1 is called an optical amplifying unit, a high-output optical amplifying device can be realized by cascading a plurality of optical amplifying units. The excitation light control according to the present invention is applied to each optical amplification unit. In addition, a variable optical attenuator that receives attenuation control for keeping the power level of output light constant is employed in the high-power optical amplifying apparatus.
[0057]
At this time, if there is at least one variable optical attenuator for a plurality of optical amplification units, the power level of the output light can be constant. In consideration of the pumping efficiency, it is desirable that the position of the variable optical attenuator is in front of the optical amplification unit at the final stage of the multistage cascade connection. This is because if the variable optical attenuator is disposed on the output side of the optical amplification unit at the final stage, the variable optical attenuator has an attenuation amount used for control, and thus it is necessary to increase the output light power of the spectral amplification unit. . That is, the optical amplifying medium requires a large pumping light power. However, when the variable optical attenuator is arranged before the final stage, amplification is performed at the subsequent stage, so that the output optical power of the optical amplifying unit immediately before the variable optical attenuator can be set low. Therefore, the optical amplifying medium of the optical amplifying unit immediately before the variable optical attenuator does not require large pumping light power. By arranging such a variable optical attenuator, it is possible to avoid preparing pump light power that is wasted in the final stage optical amplifying unit.
[0058]
When amplifying weak low-power input light, it is desirable to avoid placing an optical loss between the input port and the optical amplifying unit from the viewpoint of the noise figure of the optical amplifying device.
[0059]
Therefore, in order to realize an optical amplifying device with high output and low noise figure, it is desirable that at least one optical amplifying unit is arranged before and after the variable optical attenuator.
[0060]
FIG. 9 shows an embodiment of the fourth invention adopting such a configuration for providing a high output and a low noise figure. The optical amplifying device of FIG. 9 has a configuration of two stages of optical amplifying units, and a variable optical attenuator 200 is disposed in the middle. In FIG. 9, the input port 10 is connected to the optical isolator 120, and then the optical amplification device described in the description of the embodiment of the first invention is arranged as the first optical amplification unit. The signal light amplified by the first optical amplifying unit is output to the variable optical attenuator 200 via the optical isolator 121.
[0061]
On the output side of the variable optical attenuator 200, the optical amplifying device described in the description of the embodiment of the first invention is arranged as a second optical amplifying unit. However, backward pumping is employed in the second optical amplification unit. The second optical amplifying unit includes a rare earth-doped fiber 21 that receives the output light of the variable optical attenuator 200, a WDM optical coupler 31 that provides pump light to the rare earth-doped fiber 21, and a pump laser diode that is a light source that emits pump light. 41 and a photo detector 61 that detects the power of the pump light, an optical isolator 122 that receives the output light of the WDM optical coupler 31, and most of the output light of the optical isolator 122 is output to the output port 11. The tap coupler 101 that separates and extracts a part, the light detection unit 111 that receives the separated output light from the tap coupler 101 and detects the output light power of the rare earth doped fiber 21, the light detector 61, and the light detector The pumping light control unit 71 controls the pumping light power of the pumping laser diode 41 by inputting the detection result 111. Further, the excitation light control unit 71 includes a characteristic information table 81 and a control processing unit 91 that generates a drive signal for the excitation laser diode 41. The signal light amplified by the present optical amplifying device is output to the transmission line via the output port 11.
[0062]
The monitoring amount output from the photodetector 111 of the second optical amplification unit is input to the attenuation amount control unit 210 that controls the attenuation amount of the variable optical attenuator 200. The attenuation amount control unit 210 controls the attenuation amount of the variable optical attenuator 200 so that the output optical power of the output port 11 becomes constant at a predetermined value.
[0063]
By the way, depending on the optical transmission system, the power per channel of the optical output of the WDM signal light transmitted to the transmission path may be determined. In this case, if the number of channels is m and the power per channel is Po, the power of the optical output to the transmission line is mPo.
[0064]
When the optical amplifying apparatus used in such an optical transmission system has a mechanism for obtaining information on the number of channels of WDM signal light, that is, the number of signal lights, the optical amplifying apparatus shown in FIG. Provision of the monitoring amount to the excitation light control unit 71 can be omitted, and wiring for that purpose can be omitted. An embodiment of the fifth invention employing such a configuration is shown in FIG. The signal light number information is given to the characteristic information table 81 of the excitation light control unit 71 in the second optical amplification unit. In the embodiments of the present invention so far, the pumping light control unit 71 determines the pumping light power based on the monitored output light power. Therefore, the excitation light control unit 71 determines the excitation light power based on the signal light number information.
[0065]
That is, the pumping light control unit 71 has a calculating unit (not shown) that calculates a predetermined output light power value from the signal light number information, and gives the calculated value to the characteristic information table 81. The characteristic information table 81 extracts the value of the pumping light power corresponding to the calculated value of the output light power. The control processing unit 91 inputs the value of the excitation light power from the characteristic information table 81 and the monitor amount from the light detection unit 61, compares them, and if there is a difference between them, the light output of the excitation laser diode 41 A drive signal for generating the excitation light power extracted by the characteristic information table 81 is generated.
[0066]
In this way, a constant state with a minimum gain deviation is realized, and then the attenuation control unit 210 receives the monitor amount from the photodetector 111, and the output light of the optical amplifying device becomes constant at a predetermined power. Thus, the variable optical attenuator 200 is controlled.
[0067]
As a means for obtaining the number of signal lights, a method in which a maintenance person directly sets in the optical amplifying apparatus can be adopted. However, a channel counter unit is provided inside the optical amplifying apparatus, and the number of signal lights is autonomously provided by the counter unit. It is also possible to employ a method of counting. The channel counter unit can be realized simply by scanning the input signal light of the optical amplifying device on the wavelength axis and counting the number of peaks. Further, as another means for obtaining the number of signal lights, it is possible to employ a method of transmitting monitoring control light having a wavelength different from that of the signal light on the transmission line and transmitting the information on the number of signal lights on the monitoring control light. is there. In order to execute this method, the excitation light control unit 70 includes a monitoring control light interface unit (not shown) that receives the monitoring control light, and obtains signal light number information from the monitoring control light interface unit.
[0068]
By the way, in the configuration of FIG. 10, when it is not necessary to be concerned about the deterioration of the noise figure in the system, the first optical amplification unit can be omitted. FIG. 11 shows an embodiment of the sixth invention using one amplifier in which the variable optical attenuator is arranged in the preceding stage.
[0069]
The above is the embodiment of the configuration with the two-stage or one-stage optical amplifying unit. FIG. 12 shows an embodiment of the seventh invention in which the configuration is three or more stages. In the embodiment of the present invention, one stage of the optical amplifying unit is arranged in front of the variable optical attenuator 200, and n stages of the optical amplifying units are cascaded after the variable optical attenuator 200. In FIG. 12, a plurality of pump units 51-1 to 51-n are connected to n EDFs 21-1 to 21-n through WDM couplers 31-1 to 31-n, respectively, and each pump light control is performed. The units 71-1,..., 71-n are subjected to the same control as that of the above-described embodiment of the present invention, and the state with the minimum gain deviation is realized. The attenuation control unit 210 receives the monitor value output from the photodetector 111-n that detects the output optical power of the final stage EDF 21-n, controls the attenuation of the variable optical attenuator 200, and is an optical amplification device. As a whole, constant output control is performed. According to the embodiment of the present invention, an optical amplifying device that outputs high optical power can be realized.
[0070]
FIG. 13 shows an embodiment of the eighth invention in which the characteristic information table of the pumping light control unit is shared by the n-stage optical amplification units and unified. In the embodiment of the present invention, first, α₁, Α₂, ..., α_nIs a predetermined constant, and the pumping light power to the EDFs 21-1 to 21-n is sequentially α₁P_p, Α₂P_p, ..., α_nP_pThe n-stage optical amplifying units are collectively regarded as one optical amplifying unit, and the output optical power of the optical amplifying unit (that is, the output optical power of the n-th optical amplifying unit) and the above-described reference pumping light power P_pThe characteristic curve that minimizes the gain deviation in the relationship is obtained and stored in the characteristic information table 81. The excitation light control unit 91 calculates a predetermined output light power from the signal light number information using a calculation unit (not shown), and gives the value to the characteristic information table 81. The characteristic information table 81 includes a reference pumping light power P corresponding to a predetermined output light power value._pTake out. The control processing unit 91 uses the reference excitation light power P_pTo the pumping light power of the pumping laser diodes 41-1 to 41-n is α.₁P_p, Α₂P_p, ..., α_nP_pA drive signal to each pump laser diode is generated so that According to the embodiment of the present invention, it is possible to realize a multistage cascaded optical amplifying device having a simple configuration.
[0071]
Α₁= Α₂= ... = α_nAs a result, it is possible to control the pumping light power so that the output powers of the pumping laser diodes 41-1 to 41-n are equal. The configuration of the optical amplifier becomes simpler.
[0072]
【The invention's effect】
According to the present invention, it is possible to realize an optical amplifying apparatus that suppresses and amplifies the gain deviation of each signal light of wavelength multiplexing transmission even when the input optical power and the environmental temperature change. This eliminates the need for temperature stabilization components, temperature measurement components, and a control device for them, and therefore, it is possible to realize a simple and inexpensive wavelength-division-multiplexed optical amplifier with low power consumption and excellent amplification characteristics. it can. By using the optical amplifying device of the present invention, a simple and inexpensive optical communication system with excellent transmission characteristics can be constructed.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the properties of a rare earth-doped fiber clarified by the present invention.
FIG. 2 is a diagram showing the wavelength dependence of pumping light power and output light power of an optical amplifying device.
FIG. 3 is a configuration diagram for explaining an embodiment of a first invention of an optical amplifying device according to the present invention;
FIG. 4 is a configuration diagram for explaining a pumping method in the optical amplification device.
FIG. 5 is a diagram for explaining a procedure for determining pumping light power using a characteristic information table;
FIG. 6 is a flowchart for explaining a pumping light control method using a characteristic information table.
FIG. 7 is a configuration diagram for explaining an embodiment of a second invention of an optical amplifying device according to the present invention;
FIG. 8 is a configuration diagram for explaining an embodiment of a third invention of the optical amplifying device according to the invention;
FIG. 9 is a configuration diagram for explaining an embodiment of a fourth invention of the optical amplifying device according to the invention;
FIG. 10 is a configuration diagram for explaining an embodiment of a fifth invention of the optical amplifying device according to the invention;
FIG. 11 is a configuration diagram for explaining an embodiment of a sixth invention of the optical amplifying device according to the invention;
FIG. 12 is a configuration diagram for explaining an embodiment of a seventh invention of an optical amplifying device according to the present invention;
FIG. 13 is a configuration diagram for explaining an embodiment of an eighth invention of an optical amplifying device according to the present invention;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Input port, 11 ... Output port, 20, 21 ... Rare earth addition fiber, 30, 31 ... WDM optical coupler, 40, 41 ... Excitation laser diode, 50, 51 ... Excitation part, 60, 61, 110-112 ... Light Detector, 70, 71 ... Excitation light control unit, 80, 81 ... Characteristic information table, 90, 91 ... Control processing unit, 100-102 ... Tap coupler, 120-122 ... Optical isolator, 200 ... Variable optical attenuator, 210 ... Attenuation control unit.

Claims

An optical amplification medium that amplifies input light by the incidence of excitation light; and
A light source for generating the excitation light;
A first photodetector for detecting the excitation light power of the light source;
A second photodetector for detecting the output optical power from the optical amplification medium,
The input light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the optical amplification medium,
When the input light power, which is the sum of the multiplexed light, and the temperature of the optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. It has a characteristic information table that stores a characteristic curve in which the correspondence relationship between the output light power and the pumping light power is monotonously increased and stored,
The output light power detected by the second photodetector is collated with the characteristic information table, and a value of pumping light power corresponding to the value of the output light power on the characteristic curve is extracted from the characteristic information table. A light source control unit that controls the light source power using the extracted pumping light power value and controls the light source power so that the pumping light power value of the light source approaches the extracted pumping light power value An optical amplification device characterized by that.

An optical amplification medium that amplifies input light by the incidence of excitation light; and
A light source for generating the excitation light;
A first photodetector for detecting the excitation light power of the light source;
A second photodetector for detecting the output optical power from the optical amplification medium,
The input light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the optical amplification medium,
When the input light power, which is the sum of the multiplexed light, and the temperature of the optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. It has a characteristic information table that stores a characteristic curve in which the correspondence relationship between the output light power and the pumping light power is monotonously increased and stored,
(A) the pumping light power is detected by the first photodetector, the output light power is detected by the second photodetector, and (b) the output light power corresponding to the detected value of the output light power. Find the difference between the pumping light power value on the characteristic curve and the detected pumping light power value, and (c) the pumping light power only by the difference value or by multiplying the difference by a proportional constant. A light source control unit that controls the light source so as to change, and repeatedly performs the control of (a), (b), and (c) until the difference of (b) converges within a certain range. A characteristic optical amplification device.

On the output side of the optical amplifying medium, first light branching means for branching the output light from the medium is provided, and output light from the first output terminal of the first light branching means is Input to the second photodetector,
The output light from the second output end of the first optical branching means is input to the input end of the variable optical attenuator,
A part of the output light of the variable optical attenuator is branched and subjected to photoelectric conversion and then input to an attenuation control unit, and the attenuation control unit is configured so that the output light of the variable optical attenuator has a predetermined power The optical amplifying apparatus according to claim 1, wherein the optical amplifying apparatus is configured to control an attenuation amount of the variable optical attenuator.

A first optical isolator is provided in the front stage of the optical amplification medium so as to allow the input light to pass therethrough and prevent the reflected light from passing in the direction opposite to the propagation direction of the input light,
A second optical isolator is provided downstream of the optical amplifying medium so as to allow the output light from the optical amplifying medium to pass therethrough and prevent the reflected light from passing in the direction opposite to the propagation direction of the output light. The optical amplifying device according to claim 3, wherein:

On the output side of the optical amplifying medium, first light branching means for branching the output light from the medium is provided, and output light from the first output terminal of the first light branching means is Input to the second photodetector,
The output light from the second output end of the first optical branching means is input to the input end of the variable optical attenuator,
The output of the second optical detector is branched and input to the attenuation control unit, and the attenuation control unit attenuates the variable optical attenuator so that the output light of the variable optical attenuator has a predetermined power. The optical amplifying device according to claim 1, wherein the optical amplifying device is configured to control the optical amplifier.

A first optical isolator is provided in the front stage of the optical amplification medium so as to allow the input light to pass therethrough and prevent the reflected light from passing in the direction opposite to the propagation direction of the input light,
A second optical isolator is provided downstream of the optical amplifying medium so as to allow the output light from the optical amplifying medium to pass therethrough and prevent the reflected light from passing in the direction opposite to the propagation direction of the output light. The optical amplifying device according to claim 5, wherein

A first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, it has a first characteristic information table in which the first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is stored as data,
The first output light power detected by the second photodetector is collated with the first characteristic information table and corresponds to the value of the first output light power on the first characteristic curve. The first pumping light power value is extracted from the first characteristic information table, the first pumping light power value is used to control the first light source power, and the first light source power A first light source control unit that controls the first light source power so that the pumping light power of 1 approaches the extracted first pumping light power;
A second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light, which is the sum of the multiplexed light, and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. Has an information table,
The second output optical power value detected by the fourth photodetector is collated with the second characteristic information table, and the second output optical power value on the second characteristic curve is obtained. A corresponding second pumping light power value is extracted from the second characteristic information table, the second pumping light power value is controlled using the extracted second pumping light power value, and the second light source A second light source controller that controls the second light source power so that the second pumping light power approaches the extracted second pumping light power,
A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium,
The output of the fourth optical detector is input to an attenuation control unit, and the attenuation control unit controls the attenuation of the variable optical attenuator so that the output light of the variable optical attenuator has a predetermined power. An optical amplifying device configured as described above.

A first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, it has a first characteristic information table in which the first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is stored as data,
(A) detecting the first pumping light power by the first photodetector, detecting the first output light power by the second photodetector, and (b) detecting the detected first first power. A difference between the first pumping light power value on the first characteristic curve corresponding to the output light power value and the detected first pumping light power value is obtained, and (c) the difference The first light source is controlled so as to change the first pumping light power only by a value or a value obtained by multiplying the difference by a proportional constant, and the above (b) until the difference converges within a certain range. a) a first light source control unit that repeatedly performs the control of (b) and (c);
A second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light, which is the sum of the multiplexed light, and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. Has an information table,
(D) detecting the second pumping light power by the third photodetector, detecting the second output light power by the fourth photodetector, and (e) detecting the detected second A difference between the second pumping light power value on the second characteristic curve corresponding to the output light power value and the detected second pumping light power value is obtained, and (f) the difference The second light source is controlled so as to change the second pumping light power only by a value or a value obtained by multiplying the difference by a proportionality constant until the difference (e) converges within a certain range. a second light source control unit that repeatedly performs the control of d), (e), and (f);
A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium,
The output of the fourth optical detector is input to an attenuation control unit, and the attenuation control unit controls the attenuation of the variable optical attenuator so that the output light of the variable optical attenuator has a predetermined power. An optical amplifying device configured as described above.

The first optical amplifying medium is forward pumped, the second optical amplifying medium is backward pumped,
The signal light propagates to the front stage of the first optical amplification medium, between the first optical amplification medium and the second optical amplification medium, and to the rear stage of the second optical amplification medium, and the reflected light 9. The optical amplifying device according to claim 7, wherein an isolator is provided so as to prevent the passage.

A first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, it has a first characteristic information table in which the first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is stored as data,
The first output light power detected by the second photodetector is collated with the first characteristic information table and corresponds to the value of the first output light power on the first characteristic curve. The first pumping light power value is extracted from the first characteristic information table, the first pumping light power value is controlled using the extracted first pumping light power value, and the first light source power A first light source control unit that controls the first light source power so that the pumping light power of 1 approaches the extracted first pumping light power;
A second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light, which is the sum of the multiplexed light, and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. Has an information table,
The power per channel of the optical output of the wavelength multiplexed signal light for sending the second output light from the second optical amplification medium to the optical transmission line is determined, and the optical output power to the transmission line is a predetermined value. And
Detecting the second pumping light power by the third photodetector;
A second pumping light power value corresponding to the first predetermined value is extracted from the second characteristic information table, and the second light source power is calculated using the extracted second pumping light power value. A second light source control unit that controls and controls the second light source power so that the second pumping light power approaches the extracted second pumping light power;
A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium,
The output of the fourth optical detector is input to an attenuation control unit, and the attenuation control unit attenuates the variable optical attenuator so that the output light power of the variable optical attenuator becomes the predetermined value. An optical amplifying apparatus configured to control the light.

A first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, it has a first characteristic information table in which the first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is stored as data,
The first output light power detected by the second photodetector is collated with the first characteristic information table and corresponds to the value of the first output light power on the first characteristic curve. The first pumping light power value is extracted from the first characteristic information table, the first pumping light power value is controlled using the extracted first pumping light power value, and the first light source power A first light source control unit that controls the first light source power so that the pumping light power of 1 approaches the extracted first pumping light power;
A second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light, which is the sum of the multiplexed light, and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. Has an information table,
The power per channel of the optical output of the wavelength multiplexed signal light for sending the second output light from the second optical amplification medium to the optical transmission line is determined, and the optical output power to the transmission line is a predetermined value. And
(D) the second pumping light power is detected by the third photodetector, and (e) a second characteristic curve on the second characteristic curve corresponding to a value of a predetermined optical output power to the transmission path. The difference between the value of the pumping light power of 2 and the value of the detected second pumping light power is obtained, and (f) only the value of the difference or the value obtained by multiplying the difference by a proportionality constant The second light source is controlled to change the optical power, and the control of (d), (e) and (f) is repeated until the difference of (e) converges within a certain range. 2 light source control units,
A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium,
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The output of the fourth optical detector is input to an attenuation control unit, and the attenuation control unit attenuates the variable optical attenuator so that the output light power of the variable optical attenuator becomes the predetermined value. An optical amplifying apparatus configured to control the light.

A wavelength multiplexing number of input signal light to the second optical amplifying medium is obtained, and a predetermined value of optical output power to the transmission line is obtained from the number and a predetermined value of power per channel. The optical amplification device according to claim 10 or 11.

12. The predetermined value of the optical output power to the transmission line is mP ₀ (where m is the number of channels and P ₀ is the power per channel). Optical amplification device.

The predetermined value of the output optical power of the variable optical attenuator is mP ₀ (where m is the number of channels and P ₀ is the power per channel). An optical amplifying device according to claim 1.

An optical amplification medium that amplifies input light by the incidence of excitation light; and
A light source for generating the excitation light;
A first photodetector for detecting the excitation light power of the light source;
A second photodetector for detecting the output optical power from the optical amplification medium,
The input light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the optical amplification medium,
When the input light power, which is the sum of the multiplexed light, and the temperature of the optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. It has a characteristic information table that stores a characteristic curve in which the correspondence relationship between the output light power and the pumping light power is monotonously increased and stored,
The power per channel of the optical output of the wavelength multiplexed signal light for sending the output light from the optical amplification medium to the optical transmission line is determined, the optical output power to the transmission line is a predetermined value,
A value of pumping light power corresponding to the predetermined value of the optical output power on the characteristic curve is extracted from the characteristic information table, and the light source power is controlled using the extracted pumping light power value. A light source control unit that controls the light source power so that the excitation light power of the light source approaches the extracted second excitation light power;
A variable optical attenuator is provided in front of the optical amplification medium,
A second photodetector for detecting the output optical power from the optical amplification medium,
The output of the second optical detector is input to an attenuation control unit, and the attenuation control unit attenuates the variable optical attenuator so that the output light power of the variable optical attenuator becomes the predetermined value. An optical amplifying apparatus configured to control the light.

An optical amplification medium that amplifies input light by the incidence of excitation light; and
A light source for generating the excitation light;
A first photodetector for detecting the excitation light power of the light source;
A second photodetector for detecting the output optical power from the optical amplification medium,
The input light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the optical amplification medium,
When the input light power, which is the sum of the multiplexed light, and the temperature of the optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. It has a characteristic information table that stores a characteristic curve in which the correspondence relationship between the output light power and the pumping light power is monotonously increased and stored,
The power per channel of the optical output of the wavelength multiplexed signal light for sending the output light from the optical amplification medium to the optical transmission line is determined, the optical output power to the transmission line is a predetermined value,
(A) detecting the pumping light power by the first photodetector; (b) a value of the pumping light power on the characteristic curve corresponding to the predetermined value; and a value of the detected pumping light power. (C) controlling the light source so as to change the pumping light power only by the difference value or by multiplying the difference by a proportionality constant, and the difference in (b) is within a certain range. A light source control unit that repeatedly performs the control of (a), (b) and (c) until convergence,
A variable optical attenuator is provided in front of the optical amplification medium,
A second photodetector for detecting the output optical power from the optical amplification medium,
The output of the second photodetector is input to an attenuation control unit, and the attenuation control unit sets the attenuation of the variable optical attenuator so that the output optical power of the variable optical attenuator becomes the predetermined value. An optical amplifying device configured to be controlled.

The light according to claim 15 or 16, wherein a wavelength multiplexing number of the input light is obtained, and a predetermined value of optical output power to the transmission path is obtained from the number and a predetermined value of power per channel. Amplification equipment.

The predetermined value of the optical output power to the transmission line is mP ₀ (where m is the number of channels and P ₀ is the power per channel). Optical amplification device.

19. The predetermined value of the output optical power of the variable optical attenuator is mP ₀ (where m is the number of channels and P ₀ is the power per channel). An optical amplifying device according to claim 1.

(1) a first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, a first characteristic information table in which a first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is converted into data and stored;
The value of the first output light power detected by the second photodetector is collated with the first characteristic information table, and the value of the first output light power on the first characteristic curve is obtained. A corresponding first pumping light power value is extracted from the first characteristic information table, the first pumping light power value is controlled using the extracted first pumping light power value, and the first light source A first amplifying unit having a first light source control unit that controls the first light source power so that the first pumping light power of the first pumping light power approaches the extracted first pumping light power;
(2) a second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light that is the sum of the multiplexed lights and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. An information table;
The value of the first output optical power detected by the fourth photodetector is collated with the second characteristic information table, and the value of the second output optical power on the second characteristic curve is obtained. A corresponding second pumping light power value is extracted from the second characteristic information table, the second pumping light power value is controlled using the extracted second pumping light power value, and the second light source A second amplifying unit having a second light source control unit for controlling the second light source power so that the second pumping light power of the second pumping light power approaches the extracted second pumping light power,
(3) A plurality of sets of the second amplifying units are connected in series, and an output terminal of the second optical amplifying medium of the second amplifying unit at the first stage is the second amplifying unit at the second stage. Optically connected to the input end of the second optical amplification medium of the amplification unit;
A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium of the second amplification unit at the first stage,
The output of the fourth photodetector of the second amplification unit at the final stage is input to an attenuation amount control unit, and the attenuation amount control unit is configured so that the output light of the variable optical attenuator has a predetermined power. An optical amplifying apparatus configured to control an attenuation amount of a variable optical attenuator.

(1) a first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, a first characteristic information table in which a first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is converted into data and stored;
(A) a value of the first pumping light power is detected by the first light detector, a value of the first output light power is detected by the second light detector, and (b) is detected The difference between the first pumping light power value on the first characteristic curve corresponding to the first output light power value and the detected first pumping light power value is obtained (c ) The first light source is controlled so as to change the value of the first pumping light power only by the difference value or a value obtained by multiplying the difference by a proportionality constant, and the difference value of (b) is constant. A first amplification unit having a first light source control unit that repeatedly performs the control of (a), (b), and (c) until it converges to a value within the range;
(2) a second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light that is the sum of the multiplexed lights and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. An information table;
(D) detecting the second pumping light power by the third photodetector, detecting the second output light power by the fourth photodetector, and (e) detecting the detected second A difference between the second pumping light power value on the second characteristic curve corresponding to the output light power value and the detected second pumping light power value is obtained, and (f) the difference The second light source is controlled so as to change the second pumping light power only by a value or a value obtained by multiplying the difference by a proportionality constant until the difference (e) converges within a certain range. a second light source control unit that repeatedly performs the control of d), (e), and (f);
The value of the first output optical power detected by the fourth photodetector is collated with the second characteristic information table, and the value of the second output optical power on the second characteristic curve is obtained. A corresponding second pumping light power value is extracted from the second characteristic information table, the second pumping light power value is controlled using the extracted second pumping light power value, and the second light source A second amplifying unit having a second light source control unit for controlling the second light source power so that the second pumping light power of the second pumping light power approaches the extracted second pumping light power,
(3) A plurality of sets of the second amplifying units are connected in series, and an output terminal of the second optical amplifying medium of the second amplifying unit in the first stage is the second in the second stage. Optically connected to the input end of the second optical amplification medium of the amplification unit;
A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium of the second amplification unit at the first stage,
The output of the fourth photodetector of the second amplification unit at the final stage is input to an attenuation amount control unit, and the attenuation amount control unit is configured so that the output light of the variable optical attenuator has a predetermined power. An optical amplifying apparatus configured to control an attenuation amount of a variable optical attenuator.

(1) a first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, a first characteristic information table in which a first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is converted into data and stored;
(A) a value of the first pumping light power is detected by the first light detector, a value of the first output light power is detected by the second light detector, and (b) is detected The difference between the first pumping light power value on the first characteristic curve corresponding to the first output light power value and the detected first pumping light power value is obtained (c ) The first light source is controlled so as to change the value of the first pumping light power only by the difference value or a value obtained by multiplying the difference by a proportionality constant, and the difference value of (b) is constant. A first amplification unit having a first light source control unit that repeatedly performs the control of (a), (b), and (c) until it converges to a value within the range;
(2) a second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light, which is the sum of the multiplexed light, and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. An information table,
The power per channel of the optical output of the wavelength multiplexed signal light for sending the second output light from the second optical amplification medium to the optical transmission line is determined, and the optical output power to the transmission line is a predetermined value. And
A second pumping light power value corresponding to the predetermined value is extracted from the second characteristic information table, and the second pumping light power value is used to control the second light source power. A second light source control unit that controls the second light source power so that the second pump light power approaches the extracted second pump light power;
A third optical amplification medium that amplifies the second output light from the second optical amplification medium by incidence of third excitation light;
A third light source for generating the third excitation light;
A fourth photodetector for detecting a third excitation light power of the third light source;
A value of the third pumping light power corresponding to the predetermined value is extracted from the second characteristic information table, and the third light source power is controlled using the extracted third pumping light power value. A second amplifying unit having a third light source control unit for controlling the third light source power so that the third pumping light power approaches the extracted third pumping light power,
(3) A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium,
The output of the fifth photodetector for detecting the output light intensity from the third optical amplifying medium provided at the final stage after the second optical amplifying medium and the attenuation control unit And the attenuation control unit is configured to control the attenuation of the variable optical attenuator so that the output light of the variable optical attenuator has a predetermined power. .

(1) a first optical amplification medium that amplifies input light by incidence of first excitation light;
A first light source for generating the first excitation light;
A first photodetector for detecting a first excitation light power of the first light source;
A second photodetector for detecting a first output optical power from the first optical amplification medium,
The input light is wavelength-multiplexed, and an optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the first optical amplification medium,
When the power of the input light, which is the sum of the multiplexed light, and the temperature of the first optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal becomes constant. However, a first characteristic information table in which a first characteristic curve in which the correspondence between the first output light power and the first pump light power is monotonically increasing is converted into data and stored;
(A) a value of the first pumping light power is detected by the first light detector, a value of the first output light power is detected by the second light detector, and (b) is detected The difference between the first pumping light power value on the first characteristic curve corresponding to the first output light power value and the detected first pumping light power value is obtained (c ) The first light source is controlled so as to change the value of the first pumping light power only by the difference value or a value obtained by multiplying the difference by a proportionality constant, and the difference value of (b) is constant. A first amplification unit having a first light source control unit that repeatedly performs the control of (a), (b), and (c) until it converges to a value within the range;
(2) a second optical amplification medium that amplifies the first output light by incidence of second excitation light;
A second light source for generating the second excitation light;
A third photodetector for detecting a second excitation light power of the second light source;
A fourth photodetector for detecting a second output optical power from the second optical amplification medium,
The first output light is wavelength-multiplexed, and the optical signal of each wavelength of the wavelength-multiplexed signal is configured to be collectively amplified by the second optical amplification medium,
When the power of the first output light, which is the sum of the multiplexed light, and the temperature of the second optical amplifying medium are variously changed, the gain deviation between the different wavelengths of the amplified optical signal is constant. The second characteristic in which the second characteristic curve in which the correspondence relationship between the output light power from the second optical amplification medium and the second pumping light power is monotonically increasing is converted into data and stored. An information table,
The power per channel of the optical output of the wavelength multiplexed signal light for sending the second output light from the second optical amplification medium to the optical transmission line is determined, and the optical output power to the transmission line is a predetermined value. And
(D) a second excitation light power of the second light source is detected by a third photodetector, and (e) a second excitation light power on the second characteristic curve corresponding to the predetermined value. And the detected second pumping light power value, and (f) changing the second pumping light power only by the difference value or by multiplying the difference by a proportional constant. The second light source that controls the second light source and repeatedly performs the control of (d), (e), and (f) until the difference of (e) converges within a certain range. A control unit,
A third optical amplification medium that amplifies the second output light from the second optical amplification medium by incidence of third excitation light;
A third light source for generating the third excitation light;
(G) detecting the third pumping light power of the third light source by a fourth photodetector, and (h) third pumping light on the second characteristic curve corresponding to the predetermined value. The difference between the power value and the detected third pumping light power value is obtained, and (i) the third pumping light power is changed by only the difference value or a value obtained by multiplying the difference by a proportional constant. The third light source is controlled so that the difference between (h) converges within a certain range, and the control of (g), (h) and (i) is repeatedly performed. A second amplification unit having a light source control unit,
(3) A variable optical attenuator is provided between the first optical amplification medium and the second optical amplification medium,
The output of the fifth photodetector for detecting the output light intensity from the third optical amplifying medium provided at the final stage after the second optical amplifying medium and the attenuation control unit And the attenuation control unit is configured to control the attenuation of the variable optical attenuator so that the output light of the variable optical attenuator has a predetermined power. .

A wavelength multiplexing number of input signal light to the second optical amplifying medium is obtained, and a predetermined value of optical output power to the transmission line is obtained from the number and a predetermined value of power per channel. The optical amplifying device according to claim 22 or 23.